How many times can the hitch head bolts be torqued?

[RFP]

In the process of setting up our Reese SC hitch, I have made several adjustments (and readjustments!) to get it 'dialed in' correctly... many of you are already so familiar with this exercise.

In the process, I have twice fully torqued the two main hitch-head-to-shank bolts to the full torque spec (250 ft. lbs.), and dang, that's tight.

Knowing next to nothing about the 'mechanical engineering' aspects of all this, I'm wondering if repeated (twice) torquing to this spec has compromised the bolts' integrity in any way.

Should I replace the bolts with new, or should I just use the ones I have and go and worry about something else?

Thanks,

Rob

[GMFL]

You are good to go. As long as they have never been over torqued they will be fine

[tjdonahoe]

Big bolts will be fine

[joel]

I agree 13 years ago I went thru all the adjusting on our first long trip. Same bolts are still in

[J. Morgan]

To the greatest extent, the only bolts that cant be tightened over and over and over are torque to yield bolts which would not be used in this application.


Talis gentium ceciderunt.

[TomKirk]

When it comes to the heavy stuff, I use grade 8 fasteners: bolts, washers, and lock nuts. Once tight, it's tight. No worries.

BTW - If your hitch bolts hafta be re-torqued, it's because they've stretched. And once stretched, they shouldn't be reused. Even grade 8 head bolts on certain motors will stretch, and as a consequence, they hafta be replaced.

Tom

[KWN306]

10 yrs ago I questioned Reese about this very situation and they told me to torque them only once. I purchased a new set of bolts when I had to change hitch height when purchasing another trailer.

250 foot pounds is a lot of torque and the material will stretch and weaken when torqued down repeatedly. I believe the new set of bolts at the time was $20+/-.

Anyhow that's my 0.02 worth.

[SteveH]

I would estimate that only one in ten hitches is adjusted perfectly the first time the bolts are tightened.

How many have you heard of breaking?

[J. Morgan]

Originally Posted by KWN306

10 yrs ago I questioned Reese about this very situation and they told me to torque them only once. I purchased a new set of bolts when I had to change hitch height when purchasing another trailer.

250 foot pounds is a lot of torque and the material will stretch and weaken when torqued down repeatedly. I believe the new set of bolts at the time was $20+/-.

Anyhow that's my 0.02 worth.

That MIGHT be the company acting in CYA mode.


Talis gentium ceciderunt.

[JCWDCW]

Quote< "BTW - If your hitch bolts hafta be re-torqued, it's because they've stretched. And once stretched, they shouldn't be reused. Even grade 8 head bolts on certain motors will stretch, and as a consequence, they hafta be replaced." >

I think the OPs point was that he had re-torqued twice while trying the zero in the adjustment, not that they had loosened off.
I believe the bolts have Belleville Washers which are dished to provide continual resistance to overcome metal creep. The bolts are usually stable but washers tend to be soft unless matched to the bolt service, and continual working will even eventually cause the metal in the hitch head to creep thus requiring a re-torque once in a while.

I had loose fittings everywhere on my hitch head after a trip to Louisiana. Had them re-tightened using an impact wrench at an RV shop. I never had that problem again in 8 years.
JCW

[Alphonse]

Originally Posted by SteveH

I would estimate that only one in ten hitches is adjusted perfectly the first time the bolts are tightened.

How many have you heard of breaking?

How many have you heard of breaking?[/QUOTE]

Actually saw some in October that were broken on a Reese. They likely had been over torqued but who knows. They were cracked at the bolt head and the hitch was a dangling mess. The owner bought new Grade 8s and put them in.

[RFP]

Originally Posted by Alphonse

Actually saw some in October that were broken on a Reese.

Yikes, that's what I have!

Originally Posted by Alphonse

The owner bought new Grade 8s and put them in.

Sounds like "cheap" insurance!

[nvestysly]

I wouldn't hesitate to tighten - loosen - tighten your screws numerous times. I've done it on our hitch a dozen times. I did it again recently when we installed new axles on the trailer and the tongue height and hitch needed to be adjusted.

Take a look at the information on the table shown HERE.

I presume you have grade 8 bolts, that's what I have and I would expect hitches to come with that hardware. The bolts on my hitch are 3/4" diameter (1-1/8 hex). The clamp load in the chart is just over 30,000 pounds!

The chart shows the torque for various friction factors of K=0.15, 0.18 and 0.20. The torque ranges from 282 - 376 LB-FT depending on the friction factor. Back when I was designing bolted joints I typically used K=0.20 as an approximation but the friction does vary depending on the material and plating. Regardless, the clamping load is intended to make the bolt act like a large rubber band - extending the bolt within it's yield curve as the nut is tightened and then returning to it's original length when the nut is loosened.

I wouldn't tighten and loosen indefinitely but a few times doesn't seem like a problem in my mind.

[MelGoddard]

Originally Posted by RFP

In the process of setting up our Reese SC hitch, I have made several adjustments (and readjustments!) to get it 'dialed in' correctly... many of you are already so familiar with this exercise.

In the process, I have twice fully torqued the two main hitch-head-to-shank bolts to the full torque spec (250 ft. lbs.), and dang, that's tight.

Knowing next to nothing about the 'mechanical engineering' aspects of all this, I'm wondering if repeated (twice) torquing to this spec has compromised the bolts' integrity in any way.

Should I replace the bolts with new, or should I just use the ones I have and go and worry about something else?

Thanks,

Rob

[From a former Premier Fastener Agent, and retired Canadian Aircraft tech; (A.M.E.);]

I advise you to replace the bolts with Grade 8 bolts, nuts, AND washers, [160 KSI STRENGTH], and torque them to the hitch mfr's spec of Grade 5 bolts. [125 KSI]. This will eliminate the possibility of stretching and bolt loosening in one case; but not another.
The other possibility is to check the fit of the hitch shank to the head mount. There is probably too much play, which will collapse inward under bolt tension and work load. This will cause loose bolts and a great chance of fatique breaking. [I measured .040"play in my Husky Hitch.]
I had a piece of .042 steel plate in hand, and after greasing it, and sharpening one edge, drove it into the space with a brass hammer.
I then torqued up my [grade 8] bolts, and have towed a heavy rig for the last six years; no problem. Check tightening the torque several times proved no looseness. It works fine, and I have a clear mind on the subject.

[MelGoddard]

Originally Posted by JCWDCW

Quote< "BTW - If your hitch bolts hafta be re-torqued, it's because they've stretched. And once stretched, they shouldn't be reused. Even grade 8 head bolts on certain motors will stretch, and as a consequence, they hafta be replaced." >

I think the OPs point was that he had re-torqued twice while trying the zero in the adjustment, not that they had loosened off.
I believe the bolts have Belleville Washers which are dished to provide continual resistance to overcome metal creep. The bolts are usually stable but washers tend to be soft unless matched to the bolt service, and continual working will even eventually cause the metal in the hitch head to creep thus requiring a re-torque once in a while.

I had loose fittings everywhere on my hitch head after a trip to Louisiana. Had them re-tightened using an impact wrench at an RV shop. I never had that problem again in 8 years.
JCW

AN IMPACT GUN?????
YIKES, ARE YOU NUTS???
An impact gun has the accuracy of a pile driver powered by a C-4 charge!
Let us know when you're going down the 401, so that I can be far behind you.
"I'd rather be an interested spectator, than an active participant"!

[MelGoddard]

Originally Posted by J. Morgan

To the greatest extent, the only bolts that cant be tightened over and over and over are torque to yield bolts which would not be used in this application.


Talis gentium ceciderunt.

And where does one FIND "Torque to yield bolts"??????

[MelGoddard]

Originally Posted by nvestysly

I wouldn't hesitate to tighten - loosen - tighten your screws numerous times. I've done it on our hitch a dozen times. I did it again recently when we installed new axles on the trailer and the tongue height and hitch needed to be adjusted.

Take a look at the information on the table shown HERE.

I presume you have grade 8 bolts, that's what I have and I would expect hitches to come with that hardware. The bolts on my hitch are 3/4" diameter (1-1/8 hex). The clamp load in the chart is just over 30,000 pounds!

The chart shows the torque for various friction factors of K=0.15, 0.18 and 0.20. The torque ranges from 282 - 376 LB-FT depending on the friction factor. Back when I was designing bolted joints I typically used K=0.20 as an approximation but the friction does vary depending on the material and plating. Regardless, the clamping load is intended to make the bolt act like a large rubber band - extending the bolt within it's yield curve as the nut is tightened and then returning to it's original length when the nut is loosened.

I wouldn't tighten and loosen indefinitely but a few times doesn't seem like a problem in my mind.

-If you remember Premier Fastener Corp. Of Euclid Ave. in Cleveland, they demonstrated, using a torque/tension tester, that the nuts should be replaced every time they were torqued to the usual 70% of the UTS.
If not, and retorqued, you would loose about 20% of your tension using the same torque.
I was an agent for Premier, and using a t/tester, a 3/8" Supertanium fastener assy.; 60 lb. ft. of torque would give us about 10,500 lbs. of tension. This was with a dry, plated assy., f/f of .18.
By loosening and retightening the nuts, we would read about 8,500 tension. Quite a drop.
Me? I replace my OEM Grade 5 bolts/nuts with Grade 8 bolts, nuts and washers, and torque them to the hitch mfr's spec of Grade 5 bolts.
That way, I'm not working the nuts to full load, and can retorque them as required.
Unfortunately, Premier seems to be out of business, in Canada, and so Supertanium bolts [220 KSI] are no longer available.
I have used Aircraft MS-21250 bolts. [220 KSI] and DSC-97 nuts in the past, but now am retired, and no longer able to access them.

[Nuvite-F]

Originally Posted by MelGoddard

And where does one FIND "Torque to yield bolts"??????

I think you used to be able to get them from the company that made special-purpose fasteners like those shown below. But I'm not sure if they're still in business.

[J. Morgan]

Originally Posted by MelGoddard

And where does one FIND "Torque to yield bolts"??????

Mostly they are used for modern engine head bolts.

Use them once and throw them away.


Talis gentium ceciderunt.

[J. Morgan]

The other modern style of fastener use is "torque angle".

Torque to a specified torque value and then advance the fastener a certain number of degrees irregardless of torque value.

This is commonly used on engine main bearing caps, connecting rod caps, etc. these fasteners can be used over and over.

I have a cool torque wrench that has gyroscopes in it for torque angle and torque to yield fasteners which are tightened in the same manner as torque angle fasteners.

Torque to yield fasteners are designed to be stretched a certain amount, ONCE, and only once. The advancement of the fastener a certain number of degrees stretches the fastener a specified amount.

Talis gentium ceciderunt.